1. Field of Invention
The present invention relates to an electro-optic device and an electronic device. In particular, the invention relates to an electro-optic device utilizing columnar spacers to keep the interval of a clearance sandwiched by two substrates at a predetermined value, and an electronic device that incorporates such an electro-optic device.
2. Description of Related Art
Electro-optic devices, such as liquid crystal display device, are typically configured by sealing liquid crystals between two substrates formed with electrodes, wiring lines and elements. Such an electro-optic device is generally provided with spacers between the two substrates to keep the interval of the clearance sandwiched between the two substrates constant (about three to five micrometers, for example) throughout the substrate surfaces. In other words, the interval is a thickness of a layer formed of liquid crystals (hereinafter xe2x80x9ccell gapxe2x80x9d). The reason why the cell gap has to be kept constant is that the display characteristics, such as the light transmittance, the contrast ratio and the response speed are adversely affected if the cell gap is not kept constant, and display unevenness is likely to be generated in a bad or the worst case.
More specifically, spacers can be used that have a fine, approximately spherical shape, for example. Many such fine, approximately spherical spacers are uniformly scattered in the liquid crystals between two substrates in the case of direct view (large) liquid crystal display devices, such as a liquid crystal television and a monitor. On the other hand, in the case of small liquid crystal display devices to zoom a light bulb of a projector, the spacers are sometimes used in the form to be mixed in a sealing material to bond two substrates.
In addition, as another example of the spacers, those having a so-called columnar shape (hereafter xe2x80x9ccolumnar spacerxe2x80x9d) can also be used (which are disclosed in JP-A-2000-66181). This is an example of spacers for use in the form that columnar members made of suitable organic materials stand together in large numbers at a proper interval on a substrate, which support two substrates by bearing force of the columns in the axial direction to keep the cell gap between the substrates constant. The proper interval is traditionally an extent that a single columnar spacer exists for a few to few tens of pixels, for example. In this connection, even in the case of using such columnar spacers, the approximately spherical spacers mixed in the sealing material (hereafter, the spacers in the sealing material are xe2x80x9cgap materialsxe2x80x9d) can be combined. Accordingly, the requirement to keep the cell gap constant can be satisfied better throughout the substrate surface.
Furthermore, the accuracy in the case of keeping the interval between the substrates constant is varied according to the difference in the twisted angle of liquid crystal molecules configuring the layer made of liquid crystals between the two substrates. For example, the requirement is about xc2x10.1 xcexcm or less in the TN (Twisted Nematic) type that the twisted angle is 90 degrees, whereas the requirement is about xc2x10.3 xcexcm or less in the STN (Super Twisted Nematic) type that the twisted angle is about 260 degrees.
However, the related art spacers are subject to the following problem. More specifically, the above liquid crystal display devices need to inject liquid crystals between two substrates, and thus a liquid crystal inlet to communicate the clearance sandwiched between the two substrates with the exterior is disposed. However, the existence of the liquid crystal inlet makes it difficult to keep the cell gap constant.
These circumstances will be described more specifically. First, the manufacture of the liquid crystal display device is largely performed as follows. The necessary features, such as electrodes, wiring lines and elements, are formed over both two substrates beforehand. Then, the sealing material mixed with the gap materials is coated around the circumference of at least one of the two substrates (sealing material coating process). Subsequently, the two substrates are bonded to each other (panel alignment process). Finally, liquid crystals are introduced into the clearance through the liquid crystal inlet by vacuuming.
In such a manufacturing processes, first, the sealing material cannot be coated over the portion to be the liquid crystal inlet in the sealing material coating process. This is because, when the sealing material is coated over the portion, liquid crystals cannot be introduced. In addition, the panel alignment process as a proper pressure is typically applied to two substrates.
Accordingly, the portion where the liquid crystal inlet exists has the cell gap that is smaller than that in the other portions. As described above, this is because two substrates are bonded as a proper pressure is utilized in the panel alignment process. Thus, the sealing material or gap materials in the sealing material generate a predetermined reaction to the substrates coming closer to each other as resisting the pressure. However, the sealing material and the gap materials are not in the portion where the liquid crystal inlet exists.
Here, even though the columnar spacers exist as the spacers between two substrates, the above problem cannot be eliminated. This is because the pressure in the panel alignment process is considerably great, and thus the reaction generated by the columnar spacers does not become equal to the reaction generated by the sealing material and the gap materials. This is more apparent by considering that the columnar spacers support the substrates by the bearing force of the columns in the axial direction as described above, that is, they support the substrate surfaces by so-called xe2x80x98pointsxe2x80x99, whereas the sealing material supports the substrate surfaces by surfaces, although the sealing material is only coated around the circumference of the substrates.
The invention may address the above and/or other problems. The invention provides an electro-optic device capable of keeping the cell gap constant throughout the substrate surfaces and even in of the liquid crystal inlet. The invention also provides an electronic device that incorporates such an electro-optic device.
In order to address or solve the above problem, a first electro-optic device of the invention has a pair of substrates formed to sandwich an electro-optic material, an inlet to communicate a clearance sandwiched by the pair of the substrates with the exterior, and a plurality of columnar spacers scattered within the surfaces of the pair of the substrates facing each other. The columnar spacers are disposed more densely in the vicinity of the inlet, and more sparsely beyond the vicinity of the inlet within the surfaces.
According to the first electro-optic device of the invention, first, the columnar keep the clearance sandwiched between the pair of the substrates at a predetermined thickness. In addition, an electro-optic material, such as liquid crystal, can be introduced from outside of the clearance to the clearance through the inlet. Then, the portion where the inlet exists is generally weaker in strength than other portions because of the formation of the port. Therefore, in the panel alignment process where a pair of substrates is bonded to each other, the portion where the inlet exists is more crushable than the other portions, and thus the cell gap becomes smaller.
Here, particularly in the invention, a plurality of the columnar spacers is disposed between a pair of substrates so as to be scattered within the surfaces in parallel to the pair of the substrates, and the columnar spacers are disposed more densely in the vicinity of the inlet and more sparsely beyond the vicinity of the inlet within the surfaces. Therefore, the reaction caused by the columnar spacers in the vicinity of the inlet becomes greater than that in the other locations. Accordingly, even though a considerably great pressure is applied in bonding the pair of the substrates to each other, the columnar spacers more densely disposed can sufficiently resist the pressure in the vicinity of the inlet.
In this connection, it is extremely difficult to scatter the approximately spherical spacers. More specifically, in order to prevent the cell gap from narrowing in the vicinity of the inlet in the form of scattering the approximately spherical spacers between a pair of substrates, the spacers need to be scattered densely in the vicinity of the inlet. However, this is extremely difficult. In view of these circumstances, the invention provides the advantage of using the columnar spacers.
Therefore, according to the invention, the clearance between a pair of substrates in the vicinity of the inlet, that is, the cell gap, can be kept at a predetermined thickness, and furthermore the cell gap can be kept at a predetermined thickness throughout the substrate surfaces. In addition, according to the electro-optic device of the invention, the possibility of adversely affecting the display characteristics, such as the light transmittance, the contrast ratio and the response speed due to the unevenness of the cell gap, can be reduced. Furthermore, the possibility of generating the display unevenness can also be decreased. Thus, the image quality can be enhanced.
Moreover, xe2x80x98the vicinityxe2x80x99 described above is the area extending over the proper range cantering the inlet. More specifically, xe2x80x98the vicinityxe2x80x99 is determined specifically in consideration that the area where the columnar spacers have to be disposed densely should be an area so as not to generate defects in images, such as display unevenness.
For example, more generally, it is sometimes observed that the display unevenness can be measured in the order of millimeter to about one centimeter. Thus, the area where the columnar spacers have to be disposed densely is determined in consideration of such circumstances. Besides, more specifically, when the image display space is two inches, a display unevenness of about five millimeters is sometimes observed. Therefore, the area in which the columnar spacers have to be disposed densely is determined as an area of about three to seven millimeters centering five millimeters for example.
In short, xe2x80x98the vicinityxe2x80x99 as described above can be determined properly by experiences, experiments, theories or simulations also including the above description.
In one embodiment of the first electro-optic device of the invention, the columnar spacers disposed in the vicinity of the inlet are disposed more densely inside a semicircular area centering the inlet within the surfaces.
According to the embodiment, the effects and advantages of the invention can be received more effectively. This is because the area where the cell gap becomes smaller generally has extended over in an approximately semicircular shape centering the inlet in the case that the cell gap in the vicinity of the inlet becomes smaller than that in the other parts, which is a problem. In other words, the portion where the inlet itself is disposed is most greatly crushed to decrease the cell gap most and the cell gap becomes gradually greater in a radial pattern starting there, or that crush occurs such that the diameter of the inlet falls into the diameter of the approximately semicircular shape or a part thereof.
However, in the exemplary embodiment of the invention, the columnar spacers are disposed more densely inside the semicircular area centering the inlet within the surfaces, and thus the distinctive unevenness of the cell gap can be eliminated more effectively. In addition, the number of the columnar spacers that have to be disposed densely can be reduced or suppressed to a minimum.
Furthermore the semicircular shape in the exemplary embodiment does not only cover a shape resulting from a perfect circle being divided along its diameter. The invention also covers various irregular shapes, such as a semielliptic shape, for example.
In short, in consideration that the specific arrangement of the columnar spacers in the vicinity of the inlet is determined from the viewpoints of how the display unevenness is reduced or prevented from being generated as described above, it should be noted that xe2x80x98the semicircular shapexe2x80x99 also has to be practically considered from such a viewpoint.
In another embodiment of the first electro-optic device according to the present invention, pixel electrodes arranged in a matrix shape and switching elements connected to each of the pixel electrodes are provided over a first substrate, which is one of the pair of the substrates, and the columnar spacers disposed in the vicinity of the inlet are arranged corresponding to each of the pixel electrodes.
According to the embodiment, a predetermined electric field can be applied to each of the pixel electrodes through the switching elements, such as a thin film transistor (hereafter xe2x80x9cTFTxe2x80x9d) or a thin film diode (hereafter xe2x80x9cTFDxe2x80x9d), thus allowing the so-called active matrix drive. In addition, a single pixel can be defined as that including at least one of the pixel electrodes and one of the switching elements is formed into one unit.
And particularly in the embodiment, the columnar spacers arranged in the vicinity of the inlet are disposed so as to correspond to each of the pixel electrodes, that is, correspond to each of the pixels. In consideration that one columnar spacer is generally disposed for a few to a few tens of pixels, it is assumed that the columnar spacers are so disposed in portions beyond the vicinity of the inlet even in the embodiment. Then, it can be said that the columnar spacers are disposed more densely in the vicinity of the inlet in the embodiment.
In this connection, the reason why one columnar spacer is disposed from a few to a few tens of pixels is for the purpose of smoothly implementing the introduction of an electro-optic material, such as liquid crystals, through the inlet. When the columnar spacers are disposed for each one of the pixels throughout the substrate surface, it becomes difficult to spread the liquid crystals to the corners of the substrates.
Moreover, to dispose the columnar spacers for each one of the pixel electrodes of course includes the case that two or more columnar spacers are disposed for one pixel electrode, depending on the circumstances, in addition to the case that one columnar spacer is disposed for one pixel electrode.
In still another embodiment of the first electro-optic device of the invention, a shading layer in the matrix shape is disposed over at least one of the first substrate and a second substrate, which is the other of the pair of the substrates, and the columnar spacers are disposed inside the width of the shading layer.
According to the embodiment, the shading layer in the matrix shape, that is, the shading layer formed in a grid shape or in a striped shape is provided, so as not to cause the reduction in the contrast ratio due to the mixed lights between the pixels. In addition, when the related art color filter is disposed, it can reduce or prevent color mixture as well.
Particularly in the embodiment, the columnar spacers are disposed inside the width of the shading layer. More specifically, the columnar spacers are disposed in the portion not directly relating to the image display. Thus, the brightness of images is not impaired, even though the columnar spacers are disposed.
Yet another embodiment of the first electro-optic device of the invention further includes an alignment layer formed on the surfaces of the pair of the substrates facing the electro-optic material, and the columnar spacer is disposed at a corner part in a crossing part inside the shading area in the matrix.
According to the embodiment, the columnar spacer is disposed near the corner part of the pixel electrode. The relationship between this and the alignment layer provided in the embodiment specifically provides at least the following effects and advantages.
More specifically, according to the embodiment, the rubbing process that is required for the alignment layer can be preferably performed. Here, the rubbing process is performed such that, after annealing, the surface of the alignment layer is rubbed with a buffing cloth wrapped around a rotating metal roller in a fixed direction. Accordingly, the alignment orientation of liquid crystals as one example of the electro-optic material can be aligned in a predetermined direction. This is because the polymer main chain of a polyimide forming the alignment layer is stretched in the rubbing direction and the liquid crystal distribution is aligned along the stretched direction.
In the meantime, the rubbing process is preferably performed uniformly throughout the surface of the alignment layer as much as possible. However, various components, such as electrodes, wiring lines and elements, are usually formed over each of the pair of the substrates, and the columnar spacers as well are particularly disposed in the invention. Therefore, it is difficult to uniformly perform the rubbing process throughout the surface of the alignment layer. This is because the various components and the columnar spacers have a vertical dimension (hereinafter xe2x80x9cheightsxe2x80x9d), thus can generate bumps and dips corresponding to the heights on the surface of the alignment layer after annealing. More specifically, even though the bumps and dips are rubbed by the rotating roller, for example, the dips cannot be rubbed sufficiently. Accordingly, the image quality is likely to be considerably adversely affected in this case.
In the embodiment, however, the columnar spacer is disposed at the corner part in the crossing part, whereby the above problem can be reduced or eliminated to a considerable extent.
More specifically, according to the arrangement of the columnar spacers in the embodiment, the peripheral part is not disposed with the columnar spacers being a nearly planar surface at other than the central part in the crossing part and the corner part in the crossing part. In such a case, the direction of the rubbing process is set in the direction from the corner part to the central part of the crossing part. Accordingly, the portions disposed behind the columnar spacers due to the xe2x80x98heightxe2x80x99 thereof, that is, the portions that are hard to subject to the rubbing process, are to be contained in the crossing part.
In the meantime, the crossing part is originally the crossing part in the shading area corresponding to the clearance between the pixel electrodes arranged in a matrix shape, and the shading layer is generally disposed in the shading area as described above. In consideration of this, it is understood that containing the portions that are not sufficiently subjected the rubbing process in the crossing part is preferable to enhance the image quality. More specifically, even though there are portions that are not sufficiently subjected to the rubbing process in the shading area, the image quality is not affected greatly. In other words, when the columnar spacers are disposed, the portions that are not sufficiently subjected to the rubbing process are generated more or less. However, according to the embodiment, a preferable rubbing process can be implemented in the sense that those portions can be contained in the portions not affecting the image display.
In addition, structure can be described wherein the crossing part is a square and the columnar spacer is disposed at the upper left corner part, which is one of the corner parts. In this case, the central part of the square and the peripheral part including the upper right corner part, the under left corner part and the under right corner part in the square have a nearly planar surface. Therefore, it is acceptable if the direction of the rubbing process in this case is in the direction from the upper left corner part to the central part or to the under right corner part with regard to the square.
Particularly, the embodiment further includes an alignment layer with a rubbing process over one of the pair of the substrates where the columnar spacers are disposed, and it is acceptable to locate the corner part at a corner on the upstream side in the rubbing direction in the crossing part over the substrate where the columnar spacers are disposed. Effects and advantages are apparent from the description above.
In still yet another embodiment of the first electro-optic device of the invention, a plurality of the inlets is provided, and the columnar spacers are disposed more densely for each of the plurality of the inlets within the surfaces.
According to the embodiment, even though the pair of the substrates has a relatively large area or diameter, for example, the cell gap between the pair of the substrates can be preferably kept at a predetermined value.
In this connection, when the substrates have a relatively large diameter, a plurality of the inlets can be disposed in order to efficiently introduce liquid crystals into the clearance between the pair of the substrates as the embodiment. In the embodiment having the plurality of the inlets in this manner, the problem of the cell gap becomes more critical due to the existence of the inlets. However, the embodiment can be preferably adapted to such a case.
Furthermore, in the above description, the large diameter is specifically where the size of the image display space in the electro-optic device is about 15 inches or greater.
A second electro-optic device of the invention has a pair of substrates formed to sandwich an electro-optic material; an inlet to communicate a clearance sandwiched between the pair of the substrates with the outside thereof; and a plurality of columnar spacers disposed as scattered within the surfaces of the pair of the substrates facing each other, the columnar spacers being disposed within the surfaces. Pixel electrodes arranged in a matrix shape are disposed over the substrate. The columnar spacers in the vicinity of the inlet are disposed corresponding to each of the pixel electrodes. The columnar spacers in other locations are disposed as one spacer for 2 to 30 of the pixel electrodes.
According to the second electro-optic device of the invention, the columnar spacers enable the space between the pair of the substrates to be maintained at a predetermined thickness, and introduce the electro-optic material, such as liquid crystals, between the pair of the substrates through the inlet, similarly to the first electro-optic device.
In addition to this, particularly in the invention, the columnar spacers in the vicinity of the inlet are disposed corresponding to each of the pixel electrodes, and the columnar spacers in other locations are disposed as one spacer for 2 to 30 of the pixel electrodes. More specifically, the arrangement density of the columnar spacers in the vicinity of the inlet is set to be greater than that in the other locations.
Therefore, the reaction caused by the columnar spacers in the vicinity of the inlet becomes greater than that in the other locations. Accordingly, even though a considerably great pressure is applied in bonding the pair of the substrates, the columnar spacers disposed more densely sufficiently resist the pressure in the vicinity of the inlet.
In addition to this, in the second electro-optic device, the arrangement density of the columnar spacers in the vicinity of the inlet is one [spacer/pixel], whereas the arrangement density in the other places is about 0.03 to 0.5 [spacer/pixel]. The former is about 2 to 33 times the latter. Therefore, the possible reaction exerted by the entire columnar spacers in the vicinity of the inlet can be considerably greater than that in the other locations, and the effects and advantages are to be exerted significantly effectively.
Therefore, according to the invention, the clearance between the pair of substrates in the vicinity of the inlet, that is, the cell gap can be kept at a predetermined thickness, and the cell gap can be kept at a predetermined thickness throughout the substrate surfaces. Furthermore, consequently, according to the electro-optic device in the invention, the possibility of adversely affecting the display characteristics, such as light transmittance, contrast ratio and response speed due to the unevenness of the cell gap, can be reduced, and the possibility of generating display unevenness can be decreased. Thus, image quality can be enhanced.
Moreover, the meaning of xe2x80x98the vicinityxe2x80x99 in the invention is the same as the description regarding the first electro-optic device.
Also in the second electro-optic device of the invention, the various embodiments described with regard to the first electro-optic device can be applied as a matter of course. More specifically, the embodiments can be adapted to the second electro-optic device such that the columnar spacers are disposed more densely inside xe2x80x98the semicircular shapexe2x80x99, they are disposed inside xe2x80x98the width of the shading layerxe2x80x99, they are disposed at xe2x80x98the corner part in the crossing area in the shading areaxe2x80x99, they are disposed at xe2x80x98the corner on the upstream side in the rubbing directionxe2x80x99, and xe2x80x98a plurality of the inletsxe2x80x99 are provided.
In another embodiment of the first or second electro-optic device of the invention, the arrangement density of the columnar spacers gradually reduces from the center of the inlet toward the outside of the center as the substrate is viewed in plan view.
According to the embodiment, the arrangement density of the columnar spacers in the immediate center of the inlet can be set P [spacer/pixel], for example, and the arrangement density of the columnar spacers in the locations considerably separate from the inlet other than in the vicinity of the inlet can be set Q [spacer/pixel]. The area generally exists that the columnar spacers are disposed at an arrangement density of X [spacer/pixel] where P greater than Q and P greater than X greater than Q are satisfied. Further generalizing this, it can be thought that the area has arrangement densities of X1, X2, . . . Xn [spacer/pixel], where P  greater than X1 greater than X2 greater than . . .  greater than Xn greater than Q is satisfied.
In addition, more specifically, the area where the columnar spacers are disposed densely is a semicircular shape can have the radius R [mm]. The embodiment is included within the scope of the embodiment that the arrangement density is P in the semicircular area of the radius r [mm] from the center of the semicircular shape, the arrangement density is Xrxe2x88x92R in the area between the outer radius of the semicircular shape having the radius r and the inner radius of the semicircular shape having the radius R, and the arrangement density is Q in the area other than the semicircular area of the radius R, where P greater than Xrxe2x88x92R greater than Q.
According to the embodiment, the columnar spacers are disposed most densely in the central portion of the inlet, which can be considered most crushable in bonding the pair of the substrates, and the columnar spacers are gradually disposed more sparsely in accordance with the likeliness to be less crushable as separate from the central portion. Therefore, the embodiment can implement the more effective, proper arrangement form of the columnar spacers to keep the cell gap constant.
An electronic device of the invention is formed to have the electro-optic device of the invention described above in order to address or solve the above and/or other problems (however, including the various embodiments).
According to the electronic device of the invention, it is formed to have the electro-optic device of the invention including the various embodiments. Thus, the cell gap between the pair of the substrates forming the electro-optic device is kept constant, whereby various electronic devices can be realized, such as a projection display device (liquid crystal projector), a liquid crystal television, a cellular phone, a personal digital assistant, a word processor, a viewfinder or monitor direct view video tape recorder, a work station, a visual telephone, a point-of-sale terminal, and a touch panel, which can display high-quality images, for example.
Exemplary effects and advantages of the invention will be apparent from the following embodiments.